<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<bindings xmlns="http://www.mozilla.org/xbl">
<binding id="a">
<content><span xmlns="http://www.w3.org/1999/xhtml">
<children xmlns="http://www.mozilla.org/xbl"/>
</span></content>
</binding>
</bindings>

<style>pre::first-letter {float: left; }
</style>
</head>
<body>
<pre style="-moz-binding: url(#a);">//</pre>
</body>
</html>